Inventors have long been concerned with devising penetration resistant panels to serve as doors for safes, vaults, and the like. A more-or-less conventional approach to penetration resistance is to pack the interior of the panel with layers of tough materials, such as, metal screen, ceramic, gypsum and mineral fibers. This is the approach advocated by U.S. Pat. No. 5,060,582 granted Oct. 29, 1991 to H. Salzer for “High Security Blast Resistant Door Leaf”.
A more sophisticated approach was suggested in U.S. Pat. No. 6,240,858 granted Jun. 5, 2001 to M. C. Mandall for “Penetration Resistant Panel”. In this patent the panel contains a plurality of elongated members in a serpentine configuration under axial compression. The serpentine members are biased to straighten and extend into an opening that is cut or blasted through the panel.
While these prior art approaches to penetration resistance are somewhat effective, there continues to be a need for an improved penetration resistance panel which is particularly effective in resisting not just one, but repeated explosive attacks. Existing systems are generally considered effective at resisting an initial explosive attack in so far as stopping an attacker from completely breeching the barrier. However the initial attack produces damage, typically leaving the internal structural members of the barrier exposed to some degree and considerably more vulnerable to additional explosive attacks. Accordingly a need exists for a panel that can survive multiple attacks without exposing internal structural members to direct attack.
In addition, with door systems involving active internal elements, such as for example the system disclosed in the '858 patent to Mandall, resisting more than one explosion requires that the internal door elements remain free to straighten and fill a hole caused by an initial explosion. The outer skin of such door panels is typically a relatively thin plate selected to minimize the potential for itself deforming into and restraining the active internal elements. A problem with such systems however, is that the need for a relatively thin outer skin conflicts with the desire to minimize the area of the inner door exposed after an explosive attack. Thus a need exists for a barrier capable of providing a significant degree of resistance to an initial explosive attack without itself damaging or encroaching upon neighboring blast resistant elements.